I like to construct an autotransformer . Input voltage .240Vsingle phase. to use in a system whose operation voltage is 120v. 15 amps 1000 watts can some suggest me as to how i should proceed in calculating size of core ,winding turns, wire sizes etc , now i have 4 inches square E type transformer core . I removed all windings from it. It was used in a microwave .
You are very much over-complicating the problem. All you need is to get an 18-volt transformer and design a 15 volt voltage regulator circuit based on it. Radio Shack has lots of books, parts, and resources to get you going. Also, check your local public or college library for electronics books. Have fun!
If the microwave transformer has a 240 volt primary winding, count the turns and use the same number of turns for the autotransformer. If it has a 120 volt primary, use twice as many turns as the original transformer. Half of the turns will carry only the primary current. The wire for those turns should be about the same size as the original wire if the primary was 240 volts or half that size if the original primary was 120 volts. The remaining turns need to be about three times the size of the first half of the turns.
